Subject matter of the present invention is an impression material for use with an impression spoon.
WO-A-97/32536 and WO-A-98/52491 describe an impression spoon and an impression material for said impression spoon.
There, the impression material is fed from the rear ends of the impression spoon into the mold cavity confined and sealed between the impression spoon and the jaw and drawn through the groove of the mold to the front end of the impression spoon under the influence of reduced pressure. An introduction of deflector elements in the form of skeleton foams results in a flow component of the impression material parallel to the tooth center promoting the complete impression of undercut and deeper areas.
Using such impression spoons, one obtains highly precise impressions whichxe2x80x94as compared to impressions obtained by conventional impression techniquesxe2x80x94do not contain any trapped liquids (sulcus liquid, blood) or air bubbles and which do not have any defective wetting, distortions, or elastic recovery of shape after the deformation of the plastic impression material under pressure.
The low-viscous impression materials used in the conventional impression techniques are not or only restrictedly usable with the new impression spoon due to the kinetic and rheological properties thereof.
The impression materials usually used in the conventional impression techniques consist of a multicomponent system:
xcex1) di- and polyalkenylsiloxanes;
xcex2) polyhydrogensiloxanes;
xcex3) a precious metal catalyst of the 8th side group of the periodic system;
xcex4) reinforcing fillers;
xcex5) non-reinforcing fillers.
The technical problem forming the basis of the invention is the provision of an impression compound which can be used in the novel impression spoons according to WO-A-97/32536 and WO-A-98/52491. Another problem is the provision of a formulation which does not sedimentate and separate during storage, the rheological properties of which remain almost unchanged and which results in a cured impression material having mechanical properties which correspond to the features of DIN 24823 (ISO 4823) as well as the required tear resistance and tear propagation resistance.
Said problem is solved by an impression material for use with an impression spoon, wherein the impression material comprises curable components and at least one first filler, characterized in that said at least one filler has a BET surface of from 20 to 50 m2/g, preferably from 30 to 40 m2/g, whereby the impression material becomes slightly thixotropic and attaining a viscosity of from 1 to 350 Pas.
The impression material of the invention is advantageous in that it meets the demands made on the use thereof in the novel impression spoon, in particular the demands made on the impression material with regard to viscosity, reaction kinetics, elastic properties and thixotropy during the flow of the material through the impression spoon. These are in particular:
a) Viscosity
The impression materials of the invention used in the novel impression spoon according to WO-A-97/32536 and WO-A-98/52491 ensure a very good flow behavior which results in an optimal impression. Studies have revealed that the impression results of said novel impression technique are the better the lower the mixed viscosity of the employed impression material is.
Preferably, low-viscous formulations having a mixed viscosity in the range of from 1 to 40 Pas are employed; especially preferred are mixed viscosities of from 1 to 10 Pas.
Low-viscous formulations in this viscosity range have been known in the art (see table 3).
The tooth impression materials having the lowest viscosity (DIN 24823, ISO 4823) obtainable on the market have a mixed viscosity of from 27 to 1100 Pas. The mixed viscosities of the impression materials having the lowest viscosity (Permadyne Garant 2:1, Provil L Panasil contact plus, and Lastic Xtra superfine) exceed the ideal viscosity range of from 1 to 10 Pas. Therefore, said materials used for the conventional impression techniques such as the correction and sandwich impressions have only unsatisfactory impression results in this novel impression technique.
b) Elastic Properties During the Flow Through the Impression Spoon (Reaction Kinetics)
In the novel impression technique according to WO-A-97/32536 and WO-A-98/52491 the impression spoon is filled from the rear to the front. An important criterion is that the mixed viscosity of the inventive impression material during the flow through the impression spoon has to remain almost constant, i.e., no or only very weak elastic properties by chemical crosslinking may be generated. Also here, the marketable products used for the conventional impression techniques (Aquasil LV, Xantopren XL, Coltene President light) have drawbacks. These products are disadvantageous in that they crosslink too fast during the flow through the impression spoon according to WO-A-97/32536 and WO-A-98/52491 and thus generate elastic properties already during the flow through the impression spoon.
When employing the conventional impression materials as such in the novel impression spoon, also this kinetic effect results in unsatisfactory impression results.
c) Thixotropy
The impression materials of the invention employed in the novel impression spoon according to WO-A-97/32536 and WO-A-98/52491 ensure that the thixotropy is as low as possible, which considerably contributes to an optimum impression. Studies have revealed that the impression results obtained with the use of this novel impression technique are the better the lower the thixotropy of the employed impression material is. Usually, the impression materials employed in accordance with prior art have thixotropic properties (e.g., Panasil contact plus, thixotropic index: 1.7).
In the novel impression technique, said impression materials revealed only unsatisfactory impression results since said impression materials form flow trails in the shadow area of the flow direction when flowing through the impression spoon from the rear to the front around the teeth.
In addition to the above-mentioned properties, the inventive impression material for the novel impression technique meets further demands which will be explained below:
The inventive impression materials for the novel impression technique according to WO-A-97/32536 and WO-A-98/52491 meet the demands of type 3 of DIN 24823 and ISO 4823, resp., with regard to the compression set in the range of from 2 to 20% and the recovery of shape after the compression in the range of from 96.5 to 100%, a linear dimensional change (polymerization shrinkage) in the range of from 0 to 1.5%, and an accuracy of reproduction of 0.02 mm.
The Shore hardness (DIN 53505, ISO 868) of the cured impression material of the invention is between a Shore A of from 30 to 50, preferably from 35 to 45, which is advantageous for the novel impression technique according to WO-A-97/32536 and WO-A-98/52491.
Some impression materials in accordance with prior art used for the conventional impression techniques have Shore A hardnesses of  greater than 50. (Aquasil LV: Shore A of 58, Coltene, President light body: a Shore A of 59). High Shore A hardnesses render the removal of the cured impression material from the mouth more difficult.
In the novel impression technique according to WO-A97/32536 and WO-A-98/52491, inventive impression materials having minimum tear resistance and tear propagation resistance values (according to DIN/EN 53504 and DIN 53515) in the cured state of from 150 N/cm2 to 250 N/cm2 and 0.5 to 2.5 N/mm, resp., are employed.
In the novel impression technique according to WO-A97/32536 and WO-A-98/52491 the teeth are reproduced faithfully in every detail, Gaps between the teeth and fissures between crowns and tooth stamps are completely filled with impression material. After the curing of the impression material, the tear resistance and tear propagation resistance values have to be so high that the impression can be removed from the mouth and the impression spoon without being destroyed. On the other side, the tear resistance and tear propagation resistance values must not be excessive in order to avoid excessive stresses on the patient""s attachment apparatus during the removal of the cured impression material from the mouth.
As mentioned above, the novel impression technique according to WO-A-97/32536 and WO-A-98/52491 makes particularly high demands on the rheological properties. Surprisingly, the impression material of the invention meets these demands.
Hereinafter, preferred embodiments of the impression material of the invention are described.
A suitable impression material for the novel impression technique has a very low mixed viscosity (between 1 and 10 Pas) and no or only very low thixotropic properties (thixotropic index xe2x89xa61.2, in particular xe2x89xa61.1).
A mixed viscosity between 1 and 10 Pas of the multi-component material, usually a two-component material, means that the viscosities of the single components are below or equal to 1 to 10 Pas and the thixotropies are below or equal to 1.2, in particular 1.1.
Contrary to the single components of impression materials according to prior art having no or a low viscosity in the above mentioned viscosity range of from 1 to 10 Pas, the impression materials of the invention are not prone to a sedimentation of the fillers and a separation of the polymers or softeners in the storage time.
The storage stability of dental impression materials in primary packages should be at least from 18 months to 36 months. In this time said separation and sedimentation phenomena may not occur since the features of quality of the impression material will suffer otherwise. Further, the adjusted rheological properties may only vary within narrow tolerances in the storage time in order to ensure the required flow properties.
Above all, the poststiffening phenomenon frequently occurring in the practice, i.e., the increase of viscosity and thixotropy in the storage time, should be avoided as far as possible.
A certain, easily reducable thixotropy of the single components of the inventive impression material is acceptable and even advantageous for the storage stability with regard to sedimentation and separation since the filler particles are kept in suspension in thixotropic single components.
The requirement for this is that the thixotropy of the single components affects the thixotropy of the mixed impression mass since the flowability of the impression material in the novel impression spoon will be impaired otherwise.
The impression material according to the invention meets the following demands:
The mixed viscosity is between 1 and 350 Pas, the impression material does not or nearly not have thixotropic properties, the rheological properties remain nearly constant in the storage time, and no sedimentation or separation occurs in the storage time.
Further, the mechanical properties of the cured impression material concerning the tear resistance, tear propagation resistance, Shore A hardness, and the requirements of DIN EN 24823 (ISO 4823) meet the demands stated above.
In a preferred embodiment, the mixed viscosity is from 1 to 40 Pas, in particular preferably from 1 to 10 Pas. In order to realize the required mixed viscosities of from 1 to 350 Pa, in particular from 1 to 40 Pas, preferably from 1 to 10 Pas, the single viscosities of the single components of a two-component impression material have to be within the mentioned limits. Moreover, it is also possible that one single component has a very high viscosity and the other one a very low viscosity. According to the invention, the mixture must have a viscosity of from 1 to 350 Pas, in particular from 1 to 40 Pas, preferably from 1 to 10 Pas in this case.
According to the invention, a low-viscous, non-thixotropic impression material which has a mixed viscosity within the above-mentioned limits and a thixotropic index of from 1.0 to 1.2 and rheological properties remaining unchanged during the storing, which does not sedimentate in the storage time and has mechanical properties after curing meeting the features required according to ISO 4823 and the required tear resistance and tear propagation resistance can be produced.
Preferably, this can be achieved by using a first inorganic filler having a BET surface between 20 and 50 m2/g, which may be hydrophobized, in the impression material of the invention.
Especially preferred is a combination of said inorganic filler with a reinforcing inorganic filler having a BET surface which is greater than that of the first filler and which is preferably between 50 to 700 m2/g, in particular from 110 to 170 m2/g.
Another subject matter of the present invention is a filler combination of a first and a second filler, wherein the first inorganic filler has a BET surface of from 20 to 50 m2/g and the second filler is an inorganic reinforcing filler having a greater BET surface than the surface of the chosen first filler. Preferably, the second filler has a BET surface of from 50 to 700 m/g, in particular from 110 to 170 m2/g.
In particular, the inorganic filler of the invention has the following features:
The density is of from 2.0 to 2.2 g/cm3, the BET surface is of from 20 to 50 m2/g, in particular from 30 to 40 m2/g, e.g., about 35 m2/g. Due to the production-engineering conditions, the BET surface has a fluctuation range, the mean value of which is here Taken as a base. Typically, the fluctuation range is of from xc2x15 to 15 m2/g. The dibutyl phthalate adsorption according to DIN 53601 is from 140 to 180 g/100 g. The oil adsorption according to DIN ISO 7875 is from 35 to 60 g/100. The mean particle size is from 0.5 to 20 xcexcm.
Preferably, the inorganic filler of the invention is a wet-precipitated silicic acid or a naturally occurring silicic acid. As compared to pyrogenic silicic acid, said acids may have a relatively high water content of from 2 to 8%.
The inorganic fillers of the invention consist of from 80 to 100% of silicon dioxide. Further, they may comprise other metal oxides such as aluminium oxide, calcium oxide, sodium oxide, potassium oxide, iron oxide, and titanium oxide. Especially preferred as metal oxides in addition to silicon dioxide are calcium oxide, sodium oxide, potassium oxide, and aluminium oxide.
In particular, the hydrophobized silicic acid whichxe2x80x94according to the inventionxe2x80x94has to be employed in combination with the inventive inorganic reinforcing filler having a BET surface of from 20 to 50 m2/g has the following characteristics:
The density is between 2.0 and 2.2 g/cm3, the BET surface is from 110 to 170 m2/g, in particular between 130 and 150 m2/g.
The primary particle size is between 5 and 30 nm.
The hydrophobized, highly dispersed silicic acid is preferably prepared by a flame hydrolysis of silicon tetrachloride.
Said highly dispersed silicic acid is a hydrophobized, highly dispersed silicic acid being a synthetic, X-ray amorphous silicon dioxide.
The hydrophobized, highly dispersed silicic acid is preferably surface-treated with trimethylsilyl groups. The degree of hydrophobicity is characterized by a carbon content of from 1 to 6% and preferably between 2 and 3%.
In the production, said hydrophobized silicic acid is preferably subjected to an additional refining step, an intense mechanical treatment by a pan mill or a ball mill.
The impression material of the invention on the basis of addition crosslinking silicones for the impression technique employing the novel impression spoon preferably consists of the following ingredients:
xcex1) di- and polyalkenylsiloxanes;
xcex2) polyhydrogensiloxanes;
xcex3) a precious metal catalyst of the 8th side group of the periodic system;
xcex4) optionally a reinforcing filler in the form of a hydrophobized, highly dispersed silicic acid having a BET surface of from 110 to 170 m2/g;
xcex5) an inorganic filler having a BET surface of from 20 to 50 m2/g which may be hydrophobized,
and optionally auxiliary agents such as softeners, surfactants, dyes, and polyether-siloxane copolymers which optionally contain vinyl or SiH groups.
Usually, the ingredients are divided into two separated components:
For example:
A component xcex1)+xcex3)+xcex5)+xcex4)
B component xcex2)+xcex5)+optionally xcex1).
An Especially Preferred Impression Material of the Invention Has the Following Composition of Ingredients:
xcex1) xcex1,xcfx89-vinyl-terminated polydimethylsiloxanes in a percentage range of from 40 to 80%, in particular from 50 to 70%;
xcex2) polyhydrogenpolydimethylsiloxanes having at least 2 SiH groups or a SiH contents of from 0.1 to 15 mmol/g in a percentage range of from 2 to 40%, in particular from 10 to 30%;
xcex3) hydrosilylation catalysts, salts, complex and colloidal forms of the transition metals of the 8th side group of the periodic system, preferably the platinum, palladium, and rhodium metals, in particular platinum catalysts prepared from, e.g., hexachloroplatinic acid, or from platinum salts (Karstedt catalysts) in a percentage range of from 0.0001 to 0.1%, in particular from 0.0005 to 0.1%, based on the pure metal;
xcex4) optionally a reinforcing filler in the form of hydrophobized, highly dispersed silicic acid having a BET surface of from 130 to 150 m2/g in a weight range of from 0 to 30%;
xcex5) an inorganic filler having a BET surface of from 30 to 40 m2/g which may be hydrophobized in a percentage range of from 10 to 50%, in particular from 20 to 30%.
It has been known that the platinum catalyst is irreversibly destroyed already in the presence of low concentrations of acids, bases, or water. This becomes apparent during a longer storage under mom temperature conditions after about 6 months or during a temperature stress test, e.g., at 60xc2x0 C., already after 1 to 2 weeks in that the crosslinking reaction of the two-component mixture is strongly retarded or fails completely.
This effect cannot be tolerated for a dental impression material. Acids, water, and, above all, bases initiate the cleavage of hydrogen from hydrogenpolysiloxanes.
This results on the one hand in a swelling of the primary package due to the development of hydrogen gas and on the other hand in a delayed crosslinking reaction and a weakening of the cured silicone rubber during the addition reaction of the two-component material due to missing SiH functionalities.
Surprisingly, according to the invention also inorganic fillers having a BET surface of from 20 to 50 m2/g having a high water content of up to 10% and/or a very high pH value of up to 11 may be used.
After the drying of said fillers, formulations of addition crosslinking silicones with said fillers are stable.
The A component of a two component impression material containing the platinum catalyst does not exhibit any impairment of the setting kinetics in the storage time of up to 36 months. In the B component containing polyhydrogensiloxanes no development of hydrogen can be detected in this storage time.
The impression material of the invention (see examples 27, 33) is distinguished by a very good flowability. The mixed viscosity is adjustable between 1 and 40 Pas depending on the chain length of the employed silicone polymers; especially good impression results may be obtained with mixed viscosities between 1 and 10 Pas.
In the mixed state the impression material has no relevant thixotropic properties. The mixed viscosity and the non-relevant thixotropic properties remain nearly unchanged in the storage time.
The use of the inorganic filler of the invention prevents the sedimentation of the filler and the separation of the silicone polymers in the storage time of up to 36 months at room temperature.
With the impression material of the invention, the setting characteristics of the impression material may be adjusted within wide ranges in a matter known as such, e.g., by employing and selecting inhibitors.
The processing time, i.e., the time required by the impression material to flow through the novel impression spoon, is between 20 and 120 s, preferably between 25 and 60 s.
After the complete filling of the novel impression spoon within the mouth of the patient the impression material cures within 2.0 to 10.0 min. Curing times between 2.0 and 4.0 min are especially preferred since they reduce the expenditures in time of the attending dentist and the stress of the patient.
With respect to the impression materials in accordance with prior art, the impression material of the invention is distinguished in that the mixed viscosity thereof during the flow through the impression spoon remains nearly constant, i.e., the reaction kinetics is adjusted such that no or only very weak elastic properties by chemical crosslinking are created in the flow time. After termination of the flow stadium, the impression material of the invention preferably cures very fast (snap effect). The mechanical properties of the impression material of the invention meet the requirements of DIN EN 24823 (ISO 4823). The recovery of shape after deformation is between 96.5 and 100.0%, in particular between 99.0 and 100%. The compression set is between 2.0 and 20.0%, in particular between 5.0 and 15.0.
The Shore A hardness of the impression material of the invention is between 30 and 50, in particular between 35 and 45. The tear resistance and the tear propagation resistance of the impression material of the invention are between 150 and 250 N/cm2 and between 0.5 and 2.5 N/mm, resp. After the curing of the impression material, these mechanical properties of the impression material of the invention ensure a non-destructive removal of the impression spoon from the mouth of the patient and a removal of the impression from the impression spoon. On the other side, the mechanical properties are designed such that any damage of the patient""s attachment apparatus during the removal from the mouth is excluded.
In the following, the individual components of the impression materials of the invention will be investigated in order to illustrate the significance of the blends and the optimization thereof.
a) Formulations comprised of a vinylsiloxane, a SiH siloxane, and a platinum catalyst which do not contain any filler; in the formulations thereof, the chain lengths of the employed silicone polymers within the individual components may vary such that the mixed viscosity is within the above-mentioned limits, especially preferred from 1 to 10 Pas. The mixture of such formulations has very good flow properties. There is no thixotropy.
However, the mechanical properties of the cured impression material are completely insufficient independent of the degree of crosslinking (see comparative example 3).
In all of the following examples, the maximum possible concentration of reinforcing or non-reinforcing fillers being adjustable at the upper limit of the mixed viscosity was added.
In all cases, silicic acids and fillers hydrophobized with trimethylsilyl groups were employed in order to obtain a maximum compatibility with the silicone matrix,
b) Formulations comprised of a vinylsiloxane, a SiH siloxane, a Pt catalyst, and reinforcing fillers.
Here, the following becomes apparent:
With low and high concentrations of the highly-dispersed silicic acid (reinforcing filler) the required mixed viscosities as described under a) are attained, however, although the mechanical properties as compared to
a) are substantially improved, they are not satisfactorily met (see comparative examples 6 and 24).
c) Formulations comprised of a vinylsiloxane, a SiH siloxane, a Pt catalyst, and non-reinforcing fillers.
The desired mixed viscosities are attainable even with high concentrations of non-reinforcing fillers, however, the mechanical properties are not suited for an application in the novel impression technique. Moreover, the employed non-reinforcing fillers sedimentate in the storage test (see comparative examples 7, 8, 9).
d) Formulations comprised of a vinylsiloxane, a SiH siloxane, a Pt catalyst, and a combination of a reinforcing filler and a non-reinforcing filler.
d1) In a first borderline case of possible combinations, a high concentration of a reinforcing filler and a low concentration of a non-reinforcing filler are used.
The required mixed viscosity is adjustable, however, the mechanical properties of the cured impression material are also insufficient. Moreover, already in this case a tendency of a sedimentation of the non-reinforcing fillers in the storage test occurs (see comparative examples 10, 11, and 12).
d2) In a second borderline case, a low concentration of a reinforcing filler is combined with a high concentration of a non-reinforcing filler.
The required mixed viscosity is adjustable, however, the mechanical properties of the cured impression material are not suitable for the use with the novel impression technique. Moreover, a heavy, not acceptable sedimentation occurs in the storage test (see comparative examples 16, 17, 18, 9, 20, and 21).
d3) With the use of medium concentrations of non-reinforcing and reinforcing fillers, the required mixed viscosity may be adjusted as well.
In the storage time the mixed viscosity of the impression materials increases such that the flow properties and thus the impression result are not ensured during storage.
The cured impression material has moderate but still insufficient mechanical properties.
In the storage test, a medium sedimentation tendency is noted (see comparative examples 13, 14, and 15).
The above-mentioned embodiments reveal that none of the formulations being within the mixed viscosity range of the impression material of the invention, preferably between 1 and 10 Pas, meet the primary requirements with regard to the mechanical properties of the cured impression material and the storage stability regarding poststiffening, separation, and sedimentation.
Hence, the positive properties resulting as such from the increase of the concentrations of reinforcing and non-reinforcing fillers result in rheological drawbacks; i.e., by increasing the concentration of the reinforcing fillers the viscosity of the individual component increases drastically. In addition, the tendency of poststiffening in the storage time increases. With non-reinforcing fillers, a sedimentation of the fillers in the storage time and a separation of the polymers occurs. In addition, the tear resistance and the tear propagation resistance are impaired.
It is especially referred to the tables following the examples which summarize the results of the examples.
The invention is described in more detail in the following examples: